Gallium Nitride Based Devices For High Power Switching And Materials For Optical Applications

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Shi, Junxia

Abstract

As an essential component for all power electronic systems, power semiconductor devices have a major impact on the economy, determining the cost and efficiency of the power electronic systems. As Si based devices have approached their theoretical material limits, wide bandgap materials such as GaN and SiC are attracting a lot of interests for drastic performance improvements to meet the severe operation requirements in the future. In addition, optical applications based on group-III nitrides have attracted tremendous interests in recent years, along with the material growth advancements. This dissertation focuses on high voltage GaN-based field effect transistors for high voltage, low loss power switching applications, as well as rare earth doping in GaN particles for optical applications. AlGaN/GaN heterostructure field effect transistors were designed, fabricated, and characterized to systematically study the effects of the key design parameters on current density and off-state breakdown voltage. However, the breakdown criterion of 1 mA/mm is impractical for real applications, because of the unacceptably high power consumption at the off state. Moreover, the lack of an appropriate surface passivation has long been a bottleneck for the GaN high voltage switching research community. To solve these problems, AlGaN/GaN metal-insulator-semiconductor heterostructure field-effect transistors were designed, fabricated and characterized, with HfO2 as the gate insulator and surface passivation. These devices exhibited breakdown voltages of 1035 V for a gate-drain spacing of 10 µm, specific on-resistances of 0.9 m-omega-cm2, ultra-low gate and drain leakage currents, and minimized current slump under pulse measurements. This is the best performance ever reported on GaN-based powerswitching devices, which efficiently combines device forward, reverse, and switching characteristics. The performance of GaN devices is evidenced for the first time to go beyond the theoretical material limit of SiC. Eu doping in GaN for optical applications was also investigated in this dissertation. The effect of growth temperature on crystallinity, Eu incorporation and luminescence was investigated, and the Eu doping concentration was extracted nondestructively by strain analysis of the correlated Raman and X-ray Diffraction data. Furthermore, electrophoretic deposition was developed to fabricate thin films out of the nanoparticles.